In recent years, a service called a cloud computing service (hereinafter referred to simply as “cloud”) has become widespread. In the cloud, computing resources such as a server, a network apparatus, and a storage are acquired as virtual resources, and a user is allowed to use the computing resources depending on the user's demand, to be charged therefor. In general, in the cloud, a plurality of users share and use virtual computing resources obtained by virtualizing physical computing resources. Such a general virtualization technology includes a server virtualization technology, and a virtualized server is referred to as a virtual machine (hereinafter referred to simply as “VM”), and computing resources of a physical server are acquired for the user depending on his/her demand and allocated to the VM in accordance with a contract therewith.
Such an environment in which the physical computing resources are allocated to a plurality of users in accordance with contracts therewith is referred to as “multitenant environment”, and in the cloud, a physical computing resource is shared by a plurality of tenants (contracting entities) while the physical computing resource is exclusively used in a related-art information system. Therefore, there has risen a problem of instability in performance due to the sharing among the plurality of users, which has not been a problem in the related-art information system. In view of such a problem, a vendor of the information system has started providing a cloud service called “managed cloud” as a cloud whose performance stability and reliability are improved.
In the managed cloud, in order to ensure the performance stability, when the physical computing resource is virtualized and acquired, the physical resource is allowed to be exclusively used without being shared so that the performance can be isolated among the tenants. Because of such a configuration for the exclusive use, it is possible to ensure the performance stability. On the other hand, the exclusive configuration inhibits effective use of resources, which has been an advantage of the virtual computing resources.
WO2008/132924 discloses a technology for optimizing a period and calculation time of a CPU to be allocated depending on a load on an application executed by the virtual machine. In WO2008/132924, a problem that “a load fluctuates” is handled by means for “randomizing a period for carrying out optimization processing”.